1. Field of the Invention
The invention relates to an optical detector, and in particular to an optical detector with decreases manufacturing costs.
2. Description of the Related Art
FIG. 1a shows a conventional optical detector, wherein a laser diode 30 emits a laser beam 31 toward an object 20 moving on a measurement surface 10. The laser beam 31 contacts the object 20 and generates a reflection beam 33 and a first scattering beam 32. The object 20 moves on an x-axis, and Doppler frequency shifts the first scattering beam 32. When the first scattering beam 32 backs to a resonance chamber (not shown) in the laser diode 30, a self-mixing effect occurs in the resonance chamber to generate an optical-electrical variation. A movement on the x-axis of the object 20 and a click motion thereof are measured via measuring the optical-electrical variation by a photodiode.
A measurement effect of the conventional optical detector is related to a first angle θ between the laser beam 31 and the measurement surface 10. With reference to FIG. 1b, when the first angle θ is close to 90°, the first scattering beam is aimed at the resonance chamber of the laser diode 30, and a self-mixing in the resonance chamber is obvious. However, the path of the laser beam 31 and the first scattering beam 32 is perpendicular to a movement direction of the object 30. Thus, the first scattering beam 32 comprises no component on the x-axis and no Doppler frequency shift.
With reference to FIG. 1c, when the first angle θ nears 0°, the first scattering beam 32 comprises sufficient component on the x-axis and an obvious Doppler frequency shift. However, as shown in FIG. 1c, the first scattering beam 32 is not aimed at the resonance chamber, there is insufficient first scattering beam 32 traveling into the resonance chamber, and self-mixing in the resonance chamber fails.